Smallest possible value of a + b + c

CAT 2020 Slot 1 · QA · Medium · Number Theory

If a,ba, b and cc are positive integers such that ab=432ab = 432, bc=96bc = 96 and c<9c < 9, then the smallest possible value of a+b+ca + b + c is

  1. A.

    56

  2. B.

    49

  3. C.

    46

  4. D.

    59

Answer

C

Explanation

Dividing ab=432ab = 432 by bc=96bc = 96: ac=43296=92    a=92c\frac{a}{c} = \frac{432}{96} = \frac{9}{2} \implies a = \frac{9}{2}c

Since aa is an integer, cc must be an even integer. Given c<9c < 9, the possible values for cc are 2,4,6,82, 4, 6, 8.

Testing each case:

  • If c=2    a=9,b=48    a+b+c=9+48+2=59c = 2 \implies a = 9, b = 48 \implies a + b + c = 9 + 48 + 2 = 59
  • If c=4    a=18,b=24    a+b+c=18+24+4=46c = 4 \implies a = 18, b = 24 \implies a + b + c = 18 + 24 + 4 = 46
  • If c=6    a=27,b=16    a+b+c=27+16+6=49c = 6 \implies a = 27, b = 16 \implies a + b + c = 27 + 16 + 6 = 49
  • If c=8    a=36,b=12    a+b+c=36+12+8=56c = 8 \implies a = 36, b = 12 \implies a + b + c = 36 + 12 + 8 = 56

The smallest possible value of a+b+ca + b + c is 46.

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